A comparative study is being made of the enzymes involved in propionic acid production by anaerobic oral microorganisms. Gas chromatographic analyses will examine the effect of glucose and lactic acid concentrations on propionic acid and acetic acid production in both pure cultures as well as mixed cultures. Identification of the enzymes responsible for the production of propionic acid will be made. Of special interest is the distribution of Methylmalonyl-CoA transcarboxylase and Methylmalonyl-CoA decarboxylase, biotin enzymes responsible for the key step in propionic acid production. Direct spectrophotometric assays are available for both enzymes and they will be looked for in a wide variety of recently isolated oral bacteria capable of producing propionic acid. Isolation and purification of representatives of these enzymes from different species will be made. Their catalytic properties as well as their protein structure, e.g. subunit structure, will be examined. The overall goal is the control of these acid producing enzymes so that their toxic effects in the oral cavity can be reduced.